Triazine derivatives are known from “Collection of Czechoslovak Chemical Communications (1969), 34(6), 1673-83,” etc., for example. However, no herbicidal activity is described for the compounds disclosed in these literatures. Although various compounds are reported as triazine-based herbicides (for example, see “The Pesticide Manual 15th Edition, 2009, published by BCPC”), they all have a 1,3,5-triazine ring. Specific examples of the 1,3,5-triazine-based agrochemicals include 2-chloro-4,6-bis-(ethylamino)-1,3,5-triazine (Simazine), 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine (Atrazin), 2,4-bis(ethylamino)-6-meltylthio-1,3,5-triazine (Simetryn), 2,4-bis(isopropylamino)-6-methylthio-1,3,5-triazine (Prometryn), and 2-(1,2-dimethylpropylamino)-4-ethylamino-6-methylthio-1,3,5-triazine (Dimethametryn). Further, as a 1,2,4-triazine-based agrochemical, there are known 4-amino-3-methyl-6-phenyl-1,2,4-triazine-5(4H)-one (Metamitron), 4-amino-6-tert-butyl-3-methylthio-1,2,4-triazine-5(4H)-one (Metribuzin), etc. It is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 8-259546 that 4-(2,4-dihalogeno-5-alkoxyphenyl)-1,2,4-triazine-3,5-dione derivatives having a hydrocarbon substituent group at 6-position have a herbicidal activity. It is disclosed in JP-A No. 5-51369 that 3,5-diaryl-6-amino-1,2,4-triazine derivatives have a herbicidal activity. It is disclosed in JP-A No. 5-32641 that 3-mercapto-1,2,4-triazine derivatives have a herbicidal activity.
However, it is not known from any literatures that 6-acyl-1,2,4-triazine-3,5-dione derivatives represented by Formula 1 below have a herbicidal activity.